#coding:utf-8
score = int (input("请输入一个分数:"))
if 100 >= score >=90:
    print ('A')
else:
    if 90 >= score >=80:
        print ('B')
    else:
        if 80 >= score >=60:
            print ('C')
        else:
            if 60 >= score >=0:
                print ('D')
            else:
                print ('输入错误！')

